The main comparisons are with Grim, because it has the same strength and routine, and Lycan, which is advanceable and in the same faction. Some other alternatives are Rototurret, Lancelot, Sagittarius, Ichi 1.0, Ichi 2.0, and NEXT Gold. Note that they are mostly Haas-Bioroid, who will likely prefer to conserve influence when they have their own options, but Jinteki and NBN will be debating the merits of splashing influence. (For a full up-to-date list of program trashers - aka destroyers - see here.)))

Costs up to 4 more (can be reduced to a total rez cost of 3 3 which still translates to more than Grim, unless you're using advancement manipulation.)

May stick out like a sore thumb if you're playing a scarce few advanceable ice.

So the question you have to ask yourself is: How much is 1 Bad Publicity worth? If the answer is at least 4, obviously pick Nebula over Grim. (Assuming influence isn't a problem, and you're not considering anything else.)

Strength 3 -> 5 is a big jump for sentries, especially in straining Mimic, Femme Fatale, Alias and Pipeline. Interestingly, they synergize with each other for the purposes of bluffing. Archer is the only Destroyer at the moment with higher strength (at great cost.) +2 strength usually means at least +2 to break.

Full comparisons:

Grim | Has been used to great effect in quick binary ETR decks to keep it active and the runner in lockdown.

Lycan •• | The biggest advantage here is that it can become a code gate, which is huge, and means you can take out their sentry breaker with it. However, it has a lower strength. Note that you can use them side by side to good effect - advancing an ice once leaves them guessing: Are they threatening a Code Gate, or a Sentry? Also consider that Wormhole is an advanceable Code Gate that can trigger pre-rezzed trash-routines with an insane 7 strength, and the same exact cost of Nebula.

Rototurret • | Cheaper and ends the run... but at 0 strength a twig breaker will stop it, and a Parasite will kill it instantly.

Lancelot • | Costs neutral influence, meaning Weyland thinks twice, but less for others, still the strength is fairly low. Most decks that go grail go all-in, so you probably already know if you're using it.

Sagittarius •• | If you're HB this is a decent alternative. Slightly weaker and relies on a trace, but if the routine fires, you can guarantee you hit at least one program with 3.

Ichi 1.0 •• | Again, if you're HB this is worth considering. A great taxing ice threatening the same effect. Often you can get it to fire once before it becomes a tax to pay. This is used in decks of the opposite archetype as those for Grim.

Ichi 2.0 ••• | Everything that was good about 1.0 is amplified in 2.0, but at a higher cost. Still, if you were willing to pay for Nebula, Ichi 2.0 falls in the same range. But, it costs 3 influence outside of HB.

Overall, it's an interesting ice, with it's own situational uses. Haas-Bioroid is unlikely to give it a moment's notice, and Weyland will debate between it and Lycan (but potentially include a mix of both.) Jinteki and NBN may not think much of it, outside of Trick of Light decks, given the plethora of other options and small upside for the cost.

I've got to say, I've tried Lycan a bunch and it just doesn't work (I even made a specialised Morph deck over here http://netrunnerdb.com/en/decklist/16661/titan-morphin-). With NRE and Yog.0 making a comeback, and Mimic being as popular as ever, I think it needs to stay in the binder for the moment. Nebula, on the other hand, I really like. Grim lost some currency when d4v1d came out unfortunately, but Nebula (especially if you can advance it a couple of times) hurts less to rez as you aren't taking that bad pub. I also like this in a deck running Wormhole (almost certainly my favourite ice of this cycle) as you can bluff between the two.
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unitled5 Jun 2015